The field of aeronautic telecommunications has been highly developed in recent years.
Conventionally, the avionic networks use a bus topology standardized in the ARINC 429 standard.
More recently, the AFDX (Avionics Full Duplex Switched Ethernet) network, developed for aeronautics is based on the switched Ethernet principle. It will be reminded that switched Ethernet networks can operate under two distinct modes which however are compatible with each other: a so-called shared mode, wherein a same physical support is shared among terminals, with a random access and frame collision detection, and a so-called switched mode, wherein terminals exchange frames by means of virtual link connections, also called virtual links, thus ensuring the absence of collisions.
The AFDX network has been standardized in the ARINC 664 standard, Part 7. A description of the AFDX network is in particular found in the document entitled “AFDX protocol tutorial” available under http://sierrasales.com/pdfs/AFDXTutorial.pdf URL as well as an introduction to virtual links in FR-A-2832011 filed on behalf the present applicant. It will be merely reminded herein that the AFDX network is full-duplex, deterministic and redundant.
By full-duplex, it is meant that each subscriber to the network (terminal, calculator) can simultaneously transmit and receive frames on virtual links. The AFDX network is deterministic in that virtual links have characteristics ensured in terms of latency terminal, physical flow segregation, bandwidth and rate. For this, each virtual link has available an end-to-end reserved path through the network. Finally, the AFDX network is redundant because the underlying Ethernet network is duplicated for availability reasons.
A subscriber to an AFDX network is directly connected to a switch of this network. Data of a subscriber are transmitted as IP packets encapsulated in Ethernet frames. Unlike the conventional Ethernet switching (using the Ethernet address of the recipient), the switching of frames on an AFDC network uses a virtual link identifier included in the frame header. When a switch receives a frame on an input port thereof, it reads the virtual link identifier and determines from its switching table the output port(s) on which the frame should be transmitted.
All the equipments on board an aircraft, in particular the different sensors distributed in the aircraft, cannot be directly connected to a switch of the AFDX network. Indeed, given the great number of relevant equipments, this would require to use a great number of such switches. Moreover, since the switches are located in avionic racks, in other words generally far from sensors, this solution would imply to use numerous and long wired connections, which would be detrimental to the apparatus mass budget.
To overcome this difficulty, it has been proposed to use frame switching devices, commonly called AFDX micro-switches which has a hub function over the downlink and a switching function over the uplink. Such a micro-switch enables the ADFX network to be extended such that remote equipments can access it. To do this, it is on the one hand connected directly to a switch of the AFDX network and on the other hand, to said remote equipments. When the AFDX micro-switch receives a frame incident over the downlink, it replicates it and transmits it to all the equipments which are connected thereto. Conversely, when the AFDX micro-switch receives a frame over the uplink, that is a frame transmitted by one of the equipments in question, this it transmitted to the AFDX switch to which it is connected.
An exemplary embodiment of AFDX micro-switch has been described in Patent application FR-A-2920623 filed on behalf of the present applicant.
FIG. 1 schematically represents an exemplary AFDX network, which is extended using an AFDX micro-switch.
The AFDX network 100 consists of a plurality of AFDX switches connected with each other by physical connections (twisted pairs) 105.
The terminals 110, being subscribers to the AFDX network, are each directly connected to an AFDX switch 120.
The remote equipments 150 are not directly connected to the AFDX network but to an AFDX micro-switch 120, via physical connections 155. On the other hand, the micro-switch 130 is directly connected to a switch of this network via a physical connection 135. It will be understood that all the micro-switch and physical connections 135, 155 represent an access network 170 for the remote equipments 150. In other words, the access network 170 enables the base AFDX network 100 to be extended to the remote equipments.
In FIG. 1 is represented a virtual link VLap connecting the subscriber terminal A to the remote equipment Ep. Frames transmitted by the terminal on this virtual link are received by the micro-switch 130 which acts as a hub over the downlink by transmitting them to all the equipments Ek, k=1, . . . , K which are connected thereto. The equipments different from the recipient Ep reject the frames in question from the virtual link identifier.
Conversely, a virtual link VLqb has been represented connecting the remote equipment Eq to the subscriber terminal B. Frames transmitted by the t remote equipment Eq on this virtual link are automatically transmitted (without header reading) by the micro-switch to the AFDX switch, SW, to which it is connected. The frames are then switched through the AFDX network by the switches 120 from the virtual link identifier contained in the frame header, until reception by the subscriber B.
FIG. 2 represents an exemplary network connecting a terminal to a plurality of equipments by means of an AFDX micro-switch.
The terminal A, designated by 210, is connected to a set of equipments 250, noted Ek, k=1, . . . , K through a micro-switch 230 but, unlike the previous example, without resorting to an AFDX network. The terminal 210 can herein be located in the vicinity of the equipments 250.
The network consisting of the micro-switch 230, the physical connections 235 and 255 is conventionally called μ AFDX network.
The operating principle of this network is similar to that of the previous example. When the terminal A transmits frames on a virtual link VLap to an equipment Ep, these are transmitted by the micro-switch to all the equipments 250, these being in charge of selecting the frames intended thereto based on the virtual link identifier. Conversely, when an equipment Ep transmits frames to the terminal B on the virtual link VLqb, the micro-switch 230 merely transfers frames it receives from the equipment in question to said terminal.
It will be understood that an μAFDX network, much like the previous AFDX network, forwards AFDX frames using a frame switching, however the switching is only performed herein over the uplink. Thus, an AFDX network, whether extended or not, an μAFDX network, can all be called AFDX frame switched networks.
Whatever the network configuration, the AFDX switches and AFDX micro-switches are like to be affected by electrical failures and electromagnetic disturbances. Even though the redundancy of the AFDX network allows to overcome these drawbacks to some extent, there is a need for making switching devices free of these.
Furthermore, the AFDX switches and AFDX micro-switches consume electric power and dissipate heat. Therefore, they cannot be installed in great numbers in confined zones of the airplane, such as the avionic rack, without resorting to a cooling system.
One object of the present invention is to extend or even to make an AFDX frame switching network using at least one frame switching device which has not the abovementioned drawbacks, that is using a frame switching device which is robust and of very low consumption.